1. Field of the Invention
The present invention relates to an image processing apparatus for executing a noise reduction process to images, and to a method for reducing noise in images.
2. Description of the Related Art
In digital style cameras and the like which produce digital images using photoelectric transducers such as CCDs, it is known that noise tends to be produced in images which are obtained, as a result of the CCD properties, when the ISO sensitivity is increased under dark photographing conditions of dark photographed objects. Noise produced in portions of images corresponding to space and skin, which require smooth gray scale, significantly lowers evaluation of images. A number of conventional noise reduction techniques have thus been proposed and put to practical use. An example of a widely used method is to smooth images by using a moving average filter to smooth the image gray scale.
However, images often contain contours (edge components), and the use of averaging filters while disregarding edge components results in the problem of blurred and indistinct contours. To solve this problem, smoothing processes which avoid contours have been proposed, but as a result of the moving average filter characteristics, the appropriate use of a smoothing process in areas with unexpected contours can still affect the contours, making it impossible to execute a satisfactory smoothing process that does not affect contours.
Meanwhile, median filters are capable of executing a smoothing process without compromising edges, but the computing process is extremely time-consuming, making this an impractical alternative. There is thus a need for a smoothing process that would involve lower computer processing demands and that would be capable of reducing the noise produced in images without causing the contours in images to become blurred and indistinct.